Studying Spanish legislation regarding renewable energy, the Royal Decree 661/2007 of May 25, for regulating the activity of production of electrical energy in special regime, states that there are two types of facilities for electricity production from solar energy:    Subgroup b.1.1. Facilities that only use solar radiation as primary energy by means of photovoltaic technology.    Subgroup b.1.2. Facilities using only thermal processes for the transformation of solar energy as primary energy into electricity. These facilities may be using equipment that uses a fuel for the maintenance of the temperature of the heat transfer fluid to compensate for the lack of solar radiation that may affect the planned delivery of energy ( . . . ).
If we attend to the needs of the Red Eléctrica Española (REE), independent company dedicated exclusively to the transport and operation of the Spanish electrical network, to carry out a secure integration of renewable plants in the electrical system, it is required that they comply with certain requirements such as: uninterrupted supply, supply quality (minimizing oscillations in the supply) and manageability.
Annex 11 RD 661/2007 reads “ . . . for the purpose of this Royal Decree, unmanageable generation is defined as one where its primary source is not controllable and cannot be stored and the associated production plants of which have no possibility of carrying out a production control following instructions from the operator of the system without incurring in a spill of primary energy, or the strength of future production is not enough to be considered as a program.
In principle, special regime generators that according to the classification established in this Royal Decree are included in the groups b.1, b.2 and b.3, as well as flowing hydraulic generators integrated in groups b.4 and b.5 are considered unmanageable, unless specific manageable assessment of a generating plant to be made by the system operator, with the consequent application of the requirements or conditions associated with said condition.”
That is, according to the RD in principle, both photovoltaic (b.1.1) and solar thermal (b.1.2) energy are regarded as unmanageable. However, REE has access and connection procedures published on its website: http://www.ree.es/transporte/procedimientos_acceso_conexion.asp.
Specifically, the data form “New special regime generators with combustion or solar thermal process” in the paragraph “Assessment of solar thermal power plants manageability” defines the criteria to be met by solar thermal power plants to be considered manageable and that are generally:    1. Being ascribed to a Generation Control Center enabled by RED ELÉCTRICA, meeting the requirements of observability and controllability by the System Operator established by the regulations for facilities over 10 MW.    2. Reliability in horizons programming of:            24 hours (strength>=90%, including probability of failure of equipment)        6 hours (strength>=95%, including probability of failure of equipment)        
Availability of mechanisms to correct deviations on program:                Indication of generation means and alternative fuel        Implementation capacity            3. Storing primary energy corresponding to the operation of the plant for 4 hours at full power. The facility should be able to provide the production stored for any of the 24 hours following the time at which the reduction ends, with a minimum efficiency of 60% of the storage/retrieval cycle.
Alternatively, that the plant is able to increase its program in at least 30% of the maximum power, under certain conditions.    4. Meeting a set of requirements in relation to the behavior with voltage disturbances.    5. In regard to other types of disturbances, and particularly to changes in the system frequency, generators and their protective equipment shall meet the requirements established on the application operating methods.
If the requirements imposed by REE are met, the solar thermal power plants would be considered manageable. Moreover, being an unmanageable source of energy results in a number of disadvantages such as, among others:                Limitation in generating capacity: RD 661/2007 Annex XI “ . . . For the unmanageable generation, the generating capacity of a facility or group of facilities that share the connection point to the network will not exceed 1/20 of the short-circuit power of the network at said point . . . ”        No participation in the system adjustment services (Article 33, RD 661/2007): “All the special regime facilities will be able to participate except for those unmanageable, prior authorization by resolution of the Directorate General for Energy and Mines Policy and enabling the system operator ( . . . )”        Guarantee of power (second additional disposition RD 661/2007): “Those facilities, if any, covered by the special regime which have opted to sell their energy freely in the market will have the right to collect a fee for power guarantee, according to Article 24.1.b, except for facilities that use an unmanageable primary energy”.        
However, there are advantages in producing electrical energy from renewable sources, such as the priority in the evacuation according to Annex XI, RD 661/2007: “( . . . ) special regime generators have priority for the evacuation of the energy produced compared to the ordinary regime generators, with particular preference for the generation of unmanageable special regime from renewable sources.
Likewise, with the aim of contributing to a secure and maximum integration of the generation of unmanageable special regime the system operator will consider as preferential those generators which technology suitability further contribute to guarantee the conditions of security and quality of supply for the power system.”
The problems of quality, continuity and supply management that are indicated for the case of Spain occur regardless of the territory wherein the plants are installed. In other countries like the United States the own electric companies are the ones that must ensure that some of the electricity sold comes from renewable sources, and is therefore of their interest that it is as manageable as possible.
The immediate consequence of the problems of manageability of photovoltaics is that governments limit the size of photovoltaic plants for generating electricity to sizes smaller than those of the solar thermal power plants (50 MW maximum for power per photovoltaic plant in the case of Spain, 5 MW in India, interest in photovoltaic project proposals between 15 and 50 MW in Arizona, up to 15 MW in the state of Nevada, 30 MW in Israel, etc.).
Gathering the characteristics of each of the two types of generation from solar radiation, we have:
I) Photovoltaic generation:                Unmanageable, does not allow thermal storage or hybridization with gas        Have priority on the evacuation of energy produced        Low reliability to meet demand peaks        Coupling without attending system requirements        Variable behavior, with significant gradients        Reduced production at demand peak periods during summer and winter. During the summer due to lower efficiency in the inverter and the cell due to high temperatures and during the winter because there are lower values of solar radiation.        Difficulty of prediction: strongly increasing error rates with the forecasted horizon        It has limitations in assignments against manageable energy        It has limitation in generation capacity that shall not exceed one twentieth (5%) of the short circuit power of the network at the connection point to the network        More oriented to cover self consumption and the excess is fed into the network        
II) Solar thermal generation:                Manageable: meeting what is defined according to data form “New special regime generators with combustion or thermal solar process ” in the subsection “Assessment of manageability of solar thermal plants”        Immunity against disturbances        Inertia and regulation        Programmable (storage+hybridization with gas up to a maximum of 12% of the total of electricity production)        Energy with a support capacity in summer peaks        Possibility of participating in adjustment services        
Taking into account the objectives established by governments of individual countries for the integration and the promotion of renewable energy, a series of efforts are demanded from administrations as well as the operators of the electrical system, and the promoters of solar plants. The latter are invited to improve the design of technologies, maximizing the contribution to management (i.e., achieving quick acting plants, energy storage . . . ).
As for the type of solar thermal technology used for said combination, all known systems (parabolic or disc collector, parabolic cylinder, Fresnel, tower . . . ) are valid and even the latest technology developed wherein the solar collectors concentrate the light directing it to optical fibers or other light guides that lead it to a receiver located on the ground. An example of this technology of concentration based on optical fiber appears in the reference: “Solar fiber optic mini dishes a new approach to the efficient collection of sunlight”, Daniel Feuermann and Jeffrey M. Gordon. Solar Energy Vol. 65, No. 3, pp. 159-170, 1999 Elsevier Science Ltd.
In the state of the art there are several developments that have combined two technologies, solar thermal and photovoltaic, but not on a large scale and to supply the network as is the case in question in this invention. For example, the document WO2009/089571 describes a parabolic reflector wherein a pipe with the heat transfer fluid and/or a photovoltaic cell is installed.
In the state of the art there are also a number of patents applied for by the company Solar Systems Pty Ltd, such as document WO 2009/152574 on which the HCPV system is protected, that consist of installing a tower similar to solar thermal towers, a receiver based on photovoltaic cells, all the energy produced being of photovoltaic type, not combined with solar thermal.
Thus, the object of this invention is focused on obtaining a solar hybrid plant that, thanks to the combination of solar thermal and photovoltaic technology, achieves a minimizing in electricity production cost, ensures the continuity and quality of supply and can be classified as a manageable generation plant, without every country regulation limiting the maximum amount of solar photovoltaic energy contribution.